Slightly more than half of the homes in the U.S. use natural gas as their main heating fuel. Natural gas is a relatively clean fossil fuel. Compared to oil and coal, the combustion of natural gas releases less sulfur dioxide and nitrogen oxides, and virtually no ash or particulate matter. Natural gas combustion does produce carbon monoxide and carbon dioxide. Consequently, the combustion of natural gas does contribute to greenhouse gas emissions and to changes in the earth's carbon cycle and climate.

Natural gas also affects the environment when it is produced, stored and transported. Because natural gas is made up mostly of methane (another greenhouse gas), small amounts of methane can sometimes leak into the atmosphere from wells, storage tanks and pipelines.

Climate change threatens health through more extreme weather events, increased air pollution, limitations on food production, increased water-borne and food-borne illnesses, and increased infectious disease vectors. For the major fossil fuels, the amounts of carbon dioxide produced for each billion Btu (British thermal units) of heat energy extracted are: 208,000 pounds for coal, 164,000 pounds for petroleum products, and 117,000 pounds for natural gas. Because natural gas is non-renewable and has relatively better environmental performance as a fuel, it will be important to conserve natural gas for the future.